Airborne pathogens form an interesting group of microbes, able to successfully disseminate, cause infection and disease. The proposed project will examine the mycobacterial factors associated with the transmission of Mycobacterium tuberculosis, one of the most important bacterial pathogens of humans. The continuing burden of M. tuberculosis infection and disease is a major public health concern, heightened by reports of drug-resistant strains and the interaction between M. tuberculosis and the human immunodecificiency virus (HIV). We will blend tools and methods from epidemiology, microbial pathogenesis and genomics in our research plan to generate new knowledge about the transmission of this important airborne pathogen. Cross-sectional and prospective cohort epidemiologic studies will be used to collect data and specimens from TB cases and their contacts. Using a combination of established microbiologic methods (sputum smear exams, culture, drug susceptibility testing, TST) and novel technologies (a cough aerosol sampling system and microarrays), we will identify the factors associated with the phenotypes of transmission and aerosolization. Using comparative genomic studies, we expect to identify specific genotypic markers correlated with these two important phenotypes. The field research will be performed at an established research site in Orizaba, Mexico, within a framework that promotes exchange of personnel and technology. Because the disease burden and applied research opportunities are in under-resourced countries, it is appropriate that the research be conducted there. We will use comparative genomic techniques developed at Stanford University to ascertain the genetic content of specific, well-characterized clones identified from the field site. Finally, we use statistical techniques and analyses to correlate specific genotypes with the observed phenotypes. We will perform a series of genomic analyses to address the question of whether all clones of M tuberculosis aerosolize equally and infection is purely opportunisitic (defined by host and environmental factors), or whether infection and disease are primarily caused by a subset of particularly aerosolizable and transmissible genotypes, unrepresentative of the population of clones as a whole.